1. Field of the Invention
The present invention relates to a loudspeaker.
The present application claims priority from Japanese Application No. 2005-280003, the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
There has been known various types of loudspeakers such as a fixed-edge speaker or a free-edge speaker. In the fixed-edge speaker, a diaphragm and an edge are integrally formed by the same material. In the free-edge. speaker, a diaphragm and an edge are formed by a separate process, and then the edge is bonded onto an outer periphery of the diaphragm. Japanese Patent Application Laid-open No. 2001-25088 discloses the free-edge speaker, in which an up-rolled edge is arranged in an outer periphery of the loud speaker and a diaphragm is arranged on an inner periphery of the up-rolled edge to be connected thereto.
A free-edge speaker 100J has a basic structure as shown in FIG. 1B. In specific, a magnetic circuit 1 includes a magnet 2, a lower plate 3, and an upper plate 4. In the magnetic circuit 1, a gap between magnetic poles is formed between the upper plate 4 and a center pole 5 which stands straight from a center position of the lower plate 3. A coil bobbin 6 which sets a voice coil 7 by winding is located so as to arrange the voice coil 7 within the gap between the magnetic poles.
A center cap 8 is mounted in the proximity of an upper end Of the coil bobbin 6. In the vicinity of the upper end of the coil bobbin 6, a center portion of a diaphragm 9 is fixed. An edge 12 is connected with an outer periphery of the diaphragm 9. A bent portion 91 is formed on the inner periphery side of the connecting portion. The diaphragm 9 is attached on an upper portion of a speaker frame 10, which is provided on the upper plate 4, through the edge 12.
On the upper portion of the speaker frame 10 is formed an outer peripheral rim 10a, which has an attaching surface 10binside it. Outside the edge 12 is formed an outer end portion 12a, which is mounted by a gasket 13 attached on the attaching surface 10b of the speaker frame 10. The outer end portion 12a is pressed down onto the attaching surface 10b by the gasket 13, which is also attached onto the attaching surface 10b, so as to be airtightly attached onto the attaching surface 10b. In addition, one end of a damper 11 is connected with the coil bobbin 6, and the other end thereof is supported by a damper supporting section 11a, which is connected with the speaker frame 10, so that the voice coil 7 can be accurately held within the gap between the magnetic poles of the magnetic circuit 1.
In such a configured loudspeaker, the coil bobbin 6 is oscillated according to driving signals supplied to the voice coil 7. The diaphragm 9, which is supported by the damper 11 and the edge 12 having a function of suspension, is oscillated by the oscillation of the coil bobbin 6, thereby reproducing sound based on sound signals supplied to the voice coil 7.
When sound signals having large amplitude are applied to the above-mentioned loudspeaker, however, the diaphragm 9 is driven at large amplitude to apply a heavy load to a bent portion 91 that is formed in a border of a connecting portion connecting the diaphragm 9 and the edge 12. As a result, there may occur strength deterioration of the diaphragm 9. If the diaphragm 9 has serious strength deterioration, the bent portion 91 may have a crack or the like so that the diaphragm 9 can be damaged.
When the sound signals having large amplitude are applied to the loudspeaker, there occurs the strength deterioration or damage of the diaphragm 9, which can deteriorate acoustic characteristics of the loudspeaker.